Calculations of electronic spectra of Fe and Co porphyrins and their anionic forms

Abstract

Energies and intensities of electronic transitions of a number of Co and Fe porphyrins and their anionic forms have been calculated by the INDO/S-CI method in the Zerner parametrization. The results from the theoretical analysis are consistent with the basic relationships observed in the change of electronic spectra within the limits of isoelectronic series of compounds characterized by identical total number of π-electrons and identical filling of the pair of d_π orbitals. It has been established that in the spectra of compounds of an isoelectronic series corresponding to the neutral state of the porphyrin ligand, the allowed electronic transitions are described by superpositions of two π → π^* configurations (la_1u → 4e_g) ) and (3a ^2u → 4e_g ) , two configurations of intermolecular charge transfer π3 (d_π → 2b_1u) and (d_π → 3b_2u), and two types of doubly excited configurations (la_1u, d_π → 4e_g, 4e_g) and (3a _2u, d_π → 4e_g, 4e_g). Data have been obtained on the energies and orbital nature of the even electronic states that are responsible for rapid exchange of excitation energy of the porphyrin molecules with the transition metals.